1. Field of the Invention
This invention relates to an apparatus and process for chemically impregnating paper and other non-woven web, and is more particularly concerned with an apparatus which applies a vacuum to the web, then delivers a chemical solution to the web in a preselected pattern, to alter or to enhance the physical characteristics of the web.
2. Description of the Prior Art
Manufacturers of products made of a non-woven web, such as paper and paperboard, have long known the desirability of treating the web with a chemical to create or enhance desired features in the product. For example, in the manufacturing of containers designed to hold liquid, such as paper milk cartons, it is essential to treat the container with a chemical sealant in order to make the carton impervious to the liquid. Other web products are chemically treated to increase their stiffness or strength. In packaging for containers or bottles, such as paper containers for soda or beer, portions of the container, but not necessarily the entire container, must be strengthened. These portions include the high stress areas such as the tops and bottoms, the heel areas, and integral carrying handles and fingerholes. In other applications, it is desirable to increase the tensile strength or tear resistance at certain areas, but not at others. These include web packaging that is intended to be opened by tearing the package in a selected area.
When, for example, the areas around the fingerholes, integral handles, or corners in a paperboard carton blank need to be reinforced, it is more economical to chemically strengthen these selected areas, only, thus conserving chemicals and so reducing per unit treatment cost. In other situations, it even can be detrimental to treat the entire web. For example, in some applications the quality of stiffness may be desirable on flat surfaces, but not in areas which must be scored to form the finished product. Applying a chemical stiffener to areas prior to their being scored, might cause these areas to crack or fracture along the score-line when folded.
Web such as cloth or paperboard have been chemically treated, or impregnated, with a variety of methods and devices utilized to impregnate the web with chemicals such as dyes, bleaches, sealants, resins, and other finishing compounds. It should be understood that the term "impregnate" as used herein, refers only to the chemical treatment or application of the chemical into the web. It is not intended that the term "impregnate" imply to what degree the web is exposed to the chemical, that is, either complete saturation of the web or decorative printing or surface coating of the web. Chemical treatment of the web can be accomplished by treating the surface of the web using a gravure press, or by using blade coating, roller coating, flexographic, silk screening or stenciling methods commonly known in the printing industry. The degree of impregnation of the web fibers using these methods is usually not as pronounced as using methods which include either relatively long exposure of the web to a chemical bath, or vacuum preparation prior to chemical treatment.
In some prior art devices, the web is driven through a chamber, and the chemical, or impregnant, is delivered under Pressure to the web. For example, in U.S. Pat. No. 4,588,616 the web is fed under a mandrel which is received in a saddle block to define a chamber with a geometrically convergent zone. As the web passes through the zone, the chemical saturant within the zone is forced under pressure into the web. Another device similar in design and function is disclosed in U.S. Pat. No. 4,411,216. U.S. Pat. No. 4,702,943 discloses chemical saturization under pressure, and also incorporates a stencil which is driven in the direction of and at the same linear speed as the web. The stencil is intended to separate selected portions of the web from a pressurized reservoir, or bath, of saturant. In this device, however, there is a possibility that unintended portions of the web could become saturated, because the stencil is exposed to the entire pressurized bath, and therefore, intimate contact of the stencil to the web is absolutely critical. This reference also discloses a device which utilizes both high and low pressure to force saturant into the web. The combination of both high and low saturant pressurization zones allows for relatively increased saturation of selected areas of the treated web. In a continuation-in-part of this reference, U.S. Pat. No. 4,740,391, the device disclosed therein also utilizes selectively aligned grooves which define even lesser pressurized saturation zones, which further reduce the amount of saturation of the web exposed to these areas. The entire web, however, is exposed to the saturant in this embodiment, when a stencil is not used. Further, the dividing line between the saturated portion and unsaturated portion of the web is abrupt. As discussed herein, the method of the present invention allows for selected degrees of impregnation and, where desirable, permits the impregnation of an area to either taper off in degree, or to end abruptly.
Other devices which deliver pressurized chemical to a web also subject the web in a prior step to a partial vacuum, in order to remove air which is held within the web. It has long been known that removing the air on the surface of and within the web allows for a higher degree of web impregnation during the treatment step. U.S. Pat. No. 3,644,137 broadly discloses the concept of subjecting the web to a partial vacuum prior to exposing the web to the chemical. U.S. Pat. No. 4,590,099 discloses an apparatus which includes a chamber divided by seals to define a low pressure preparation zone and a high pressure treatment zone. The web is subjected to the partial vacuum in the low pressure zone, and then is subjected to the pressurized saturant for the saturation of the web. The device utilizes squeeze rollers to complete an air lock to the high pressure zone, and to squeeze excess liquid from the web. The entire web is saturated in this device.
In U.S. Pat. No. 3,797,281, a different device is employed to impart a vacuum to a web prior to impregnation. The vacuum box and impregnant box, or liquor box, are juxtaposed above the web, and the chemical or impregnant is applied through a dispensing slot, as opposed to subjecting the web to a bath. A rubber sealing belt is utilized to contain the vacuum around the web. This device, however, impregnates the entire web and does not employ any means to apply the chemical to selected areas, only.
The general concept of selective application of chemical to a web is disclosed in U.S. Pat. No. 4,617,223. While this reference discusses many advantages of selective application, no specific apparatus is disclosed in detail. The method disclosed utilizes a printing or screening apparatus such as a flexographic printing process, gravure printing or stenciling.
While the prior art devices discussed disclosed various methods for saturating and impregnating a web, none discloses a highly efficient device capable of subjecting the web to a partial vacuum, then impregnating the web in a preselected pattern only. The present invention overcomes the limitations of the prior art of both printing devices and saturating devices, and further is capable of selectively treating large quantities of web per unit time in this manner.